1. Field of the Invention
This invention relates to devices and methods for transferring energy to the body with a catheter. More particularly, this invention relates to devices and methods for operating a catheter by transferring mechanical, ultrasonic and electromagnetic energy to the body.
2. Description of the Related Art
Radiofrequency (RF) ablation is widely used for treating cardiac arrhythmias. RF ablation is commonly carried out by inserting a catheter through the patient's vascular system into the heart, and bringing the distal tip of the catheter into contact with the cardiac tissue at the site that is to be ablated. RF electrical current is then conducted through wires in the catheter to one or more electrodes at the tip of the catheter, which apply the RF energy to the myocardium. The RF energy is absorbed in the tissue, heating it to the point typically about 50°-60° C.) at which it permanently loses its electrical excitability. When this sort of procedure is successful, it creates non-conducting lesions in the cardiac tissue, which disrupt the abnormal electrical pathway causing the arrhythmia.
It is often difficult to determine the proper dosage of RF energy that should be applied in an ablation procedure in order to achieve the desired result. When the dosage is insufficient, the non-conducting lesion will not extend deeply enough through the heart wall to disrupt the abnormal conduction, so that arrhythmia may persist or return after the procedure is completed. On the other hand, excessive RF dosage may cause dangerous damage to the tissue at and around the ablation site. The proper RF dosage is known to vary from case to case depending on various factors, such as catheter geometry, thickness of the heart wall, quality of the electrical contact between the catheter electrode and the heart wall, and blood flow in the vicinity of the ablation site (which carries away heat generated by the RF energy).
In order to improve the precision and consistency of RF ablation procedures, attempts have been made to predict and control the ablation based on measurement of physiological parameters of relevance.